Combustion flash lamp which can be arranged in a holder in parallel connection



March 17, 1970 L. M. NIJLAND ETAL 3,501,254

COMBUSTION FLASH LAMP WHICH CAN BE ARRANGED IN A HOLDER IN PARALLEL CONNECTION Filed Sept. 22, 1967 I 2 Sheets-Sheet 2 lumen I Ll L.l I

FIG. 6

FIG.7 00

. INVENTOR. LOUIS M. N'JLAND JOHANN SCHRODER. BY

ym/m a AGENT United States Patent 3,501,254 COMBUSTION FLASH LAMP WHICH CAN BE ARRANGED IN A HOLDER -IN PARALLEL CONNECTION Louis Marius Nijland, Emmasingel, Eindhoven, Netherlands, and Johann Schroder, Aachen, Germany, assignors, by mesne assignments, to US. Philips Corporation, New York, N.Y., a corporation of Delaware Filed Sept. 22, 1967, Ser. No. 669,888 Claims priority, application Netherlands, Sept. 30, 1966, 6613815 Int. Cl. F21k 5/02 US. Cl. 431-95 19 Claims ABSTRACT OF THE DISCLOSURE A combustion flash lamp employing a combustible metal wool and an oxidizing gas in a transparent envelope has an ignition means which permits several of these lamps to be connected in parallel to a source of transient ignition voltage so that with the application of a voltage pulse, only one lamp is ignited, and after ignition, the succeeding lamp can be ignited as required. The ignition means includes a pair of lead-in conductors connected within the lamp by an oxidizable conductive material, e.g. superficially oxidized metal powder, a semiconductor material and a binder; externally, the lead-in conductors of all lamps are connected in parallel with a pulse generator which generates heavily damped oscillations.

The invention relates to a combustion flash lamp of transparent material which contains a metal wool and an oxidizing gas which upon reaction produces actinic light, the lamp being provided with an electric ignition mechanism.

In the conventional combustion flash lamps, the metal wool generally consists of zirconium. The ignition mechanism comprises two lead-in wires which can be connected outside the bulb to a voltage source and which are interconnected inside the bulb mechanically by a bead of electrically insulating material and electrically by a filament wire. The ends of the lead-in wires or the filament wire are provided with an ignition mass which reacts exothermically when a given temperature is reached. The ignition mass generally consists of a mixture of zirconium powder, as the case may be an oxidizer, and a binder such as nitrocellulose.

Flash-lamp ignition devices are known in which a numher, for example, four or five of the flash lamps described can be arranged.

When these devices are used in combination with a camera, a number of photographs equal to the number of flash lamps provided in the holder of the device can be taken with the use of actinic light without the necessity of exchanging the flash lamps in the holder.

The known and proposed devices of this kind include switching members which are operated mechanically, electrically or by means of energy emitted by a flash lamp during its ignition.

These switching members are complicated and vulnerable and are in part of a kind such that a flash lamp which fails to ignite prevents the ignition of the remaining flashlamps in the holder.

In a parallel arrangement of members having a negative current-voltage characteristic, when the current is switched on, the voltage at one of the members will decrease to such an extent that the current is passed substantially entirely through this member. When the ignition of the flash lamps is ensured by a high voltage source, a device can be used in which the flash lamps are connected in parallel in 3,501,254 Patented Mar. 17, 1970 an electric circuit, provided that these flash lamps exhibit during the ignition process a current-voltage characteristic partly having a negative inclination and after their ignition have a very high resistance and no longer pass current.

It is an object of the invention to provide combustion flash lamps which contain as an actinically reacting material a metal wool and an oxidizing gas and which have the desired properties.

According to the invention, the combustion flash lamp having an ignition mechanism which consists of lead-in wires which may be connected outside the bulb to a current source and are interconnected inside the bulb by means of an ignition mass containing an oxidizable material and a binder is characterized in that the ignition mass comprises either a metal powder which is superficially coated with an oxide film or another oxidizable conducting material, an electrically non-conducting oxidizer, a semiconducting material and a binder, and in that the lamp includes means which screen part of the bulb wall around one or both lead-in wires from deposition of combustion products.

In the lamps according to the invention, the ignition mass is caused to react exothermically by electric breakdown through the mass and a subsequent passage of current, which results in development of heat in the mass.

In contrast to the conventional flash lamps, the reaction is not initiated by an increase in temperature resulting from passage of current through a filament wire.

The ignition is not eflected either by flash-over between one electrode and another electrode coated with the ignition mass, which is the case in a known construction.

The combustion flash lamps in accordance with the invention also differ essentially from known combustion flash lamps in which the lead-in wire of the lamps are interconnected by means of an ignition mass mainly con sisting of an oxidizable metal and a binder to which an oxidizer may be added. The essentially different composition of the ignition mass and the new geometrical construction provide the following results.

The combustion flash lamps according to the invention can be ignited not only in a simpler manner and with a smaller amount of energy and greater safety, but they' can also be connected in a simple manner in parallel in a holder. When a transient voltage pulse is applied, only one lamp ignites at a time; thus, without the use of a switching member, parallel-connected combustion flash lamps according to the invention can be ignited one after the other. This is an important advantage which has not been found in this form in any of the ignition masses used hitherto.

The ignition mass may be considered to comprise an electrically non-conducting mass of a binder, in which particles of an oxidizing agent are embedded which are also non-conducting. Between these constituents, the mass contains finely divided grains of an oxidizable metal coated with a thin oxide film acting as a junction layer and a finely divided semiconducting material both coated with a dielectric layer.

Actually, many resistance elements in the ignition mass are connected both in series and in parallel. Statistically, this results in an average overall resistance which, when the ignition mass has been provided in lamps, differs only slightly for each individual lamp. When a suitable voltage difference is applied to the lead-in wires, the reaction in the ignition mass will be initiated through a chain of resistance elements by breakdown and a subsequent passage of current, whilst heat is developed.

The applied voltage decreases in the resulting electrically good conducting reaction zone. Toward the end of the reaction, the resistance between the lead-in wires again increases to a high value.

When several flash lamps according to the invention are connected in parallel, at a transiently applied voltage, generally only one flash lamp is ignited. When the voltage is applied again, another flash lamp will be ignited. Flash lamps which cannot be ignited by means of the voltage applied, for example, owing to constructional errors, do not prevent the ignition of the remaining flash lamps.

In order to obtain a satisfactory operation of a device in which the flash lamps according to the invention are arranged in parallel connection and are ignited by means of a high-voltage source, it is desirable that, measured at a voltage of 22 v., the ignition mass should have a resistance exceeding 10 M and preferably exceeding 1000 M52. In contrast to the known ignition masses, the ignition mass used in the flash lamps according to the invention does not change when a voltage difference of a few hundreds of volts is applied between the lead-in wires.

Only when a voltage difference of approximately 1 kv. or more has been attained, breakdown and current passage occur in the mass, whereupon the mass reacts exothermically and the lamp ignites. The resistance and hence also the voltage at the exothermically reacting ignition mass then decrease very rapidly (in approximately 1 sec. below 1 kv.). Thus, the risk of two or more flash lamps being ignited simultaneously is reduced.

It is desirable that after the breakdown of the mass, the resistance of the mass should not increase owing to an increase in temperature resulting from direct passage of current before the exothermic reaction gives rise to a decrease of the resistance. This is achieved by the use of the electrically semiconducting material. The overall resistance of the ignition mass will be reduced by addition of the semiconducting material. However, with regard to the object intended, the resistance of the ignition mass in the flash lamp according to the invention will have to be at least approximately M9.

The increase in conductivity of semiconductor material resulting from an increase in temperature contributes to the desired rapid decrease of the resistance of the ignition mass after breakdown.

After the ignition, the resistance between the lead-in wires increases to a high value (approximately 1 M9 or more). The ignition of a next combustion flash lamp thus cannot give rise to a decrease of the voltage across the ignited lamps. This is also due to the geometry of the lamp. In the known combustion flash lamps, after combustion, the resistances are generally so small that after the ignition of a lamp arranged in a holder, the remaining lamps cannot ignite.

It has been found to be of advantage to add to the ignition mass a substance which acts as an activator for the reaction in the mass and causes the ignition mass to react rapidly when the temperature increases. The presence of an activator also results in a rapid decrease of the resistance of the reacting ignition mass. The risk of two or more flash lamps arranged in parallel connection ignitin-g simultaneously is thus further reduced. The risk of the ignition mass reacting not at all or not completely is also reduced. If no reaction takes place, this may be due to an unduly low reactivity and an unduly high ignition temperature of the ignition mass. An incomplete reaction may occur, for example, if the concentration of conducting material not participating in the reaction in the ignition mass is unduly high (dilution effect). If the reaction is incomplete, the reaction between the metal wool and the oxidizing gas producing actinic light can be initiated it is true, but the remaining part of the ignition mass may act as a current bridge when the shutter of the camera is opened again. This results in that no actinic light is then available for taking the photograph.

When the flash lamps according to the invention are arranged in parallel connection, the resistance between the lead-in wires of a flash lamp increases after the ignition to a value which exceeds 10 0 and is comparable with the resistance of each of the flash lamps of the arrangement still to be ignited.

Current bridges being formed between the lead-in wires upon reaction of the ignition mass must be prevented. Therefore, the ignition mass preferably contains an oxidizable material and an oxidizing agent at least in stoichiometric or substantially stoichiometric quantities, while a small excess of the oxidizable material may have a favorable effect.

A suitable ratio of the quantities of each of the constituents in the ignition mass may be readily determined by experiments. It then holds that with approximately stoichiometric quantities of oxidizing agent and constituents capable of reacting therewith, the resistance and the. breakdown voltage of the mass decrease with an increase of the content of electrically conducting material. The tolerance and the value of the breakdown voltages then also decrease. The risk of two or more flash lamps being ignited simultaneously gradually increases, however, from a given content when this content is increased. With an increasing content, the resistance finally becomes so small that the voltage at the ignition mass may decrease without resulting in ignition.

Resistances of the ignition mass in the flash lamps exceeding 10% have proved satisfactory in practice. The breakdown voltage required is then approximately thousand to a few thousands of volts, of course depending upon the composition of the ignition mass.

The energy to be supplied by the voltage source is very low, i.e. generally 10 to a few hundreds of microjoules.

When the combustion flash lamps according to the invention are arranged in a holder in parallel connection, the holder is electrically connected to the flash lamp contact of a camera and to a high-voltage generator.

This high-voltage generator must be adapted to the electrical properties of the flash lamps in the holder.

The voltage supplied 'by the generator must preferably have the form of a strongly damped oscillation, for example, of a pulse occurring approximately only once. The oscillation time must be short with respect to the shutter times of the cameras. The voltage supplied must start at a value lying below the minimum ignition voltage of the flash lamps arranged in a holder and must increase in the first place as a function of time.

A thumb rule is that the voltage generator is preferably chosen so that the average ignition voltage lies between A and A of the maximum voltage to be supplied by the high-voltage generator. With an average ignition voltage exceeding /1 of the maximum voltage to be supplied by the generator, there is a great risk of one or several flash lamps in the holder failing to ignite when the flash lamp contact is closed. This may be due to the fact that in this case the generator can no longer supply a sufficient voltage and hence no longer a sufficient quantity of energy for the breakdown and ignition of the ignition mass. With an average ignition voltage smaller than A of the maximum voltage to be supplied by the high-voltage generator, there is a great risk of two or more flash lamps being ignited simultaneously when the flash-lamp contact is closed. In this case, the energy to be supplied by the generator often suffices to ignite several flash lamps.

The ignition voltage is chosen to be so high that when the voltage is applied, the possibility of two or more lamps at a time or of no lamp at all being ignited is excluded. The minimum value is approximately 1000 v. Upon breakdown, the voltage rapidly falls below said value.

The maximum voltage to be supplied by the high-voltage generator is limited by the voltage at which discharges occur outside the lamp, for example, between the lead-in wires. When no special steps are taken, which are not absolutely necessary, however, for a satisfactory operation of the holder, this maximum voltage will be approximately 4000 to 5000 v. The energy supplied by the generator when the contact is closed must be suflicient to ignite one arbitrary flash lamp in the holder but not considerably higher.

A generator the voltage of which is sinusoidal and has a pulse width of the order of to 1000 microseconds is suitable for the object aimed at.

In principle, all the elements which produce much energy upon oxidation, such as aluminum, magnesium, zirconium, lanthanum, titanium, niobium and thorium, are suitable for use in the preparation of the ignition mass. These non-noble metals are poor conductors in the pulverulent state, since the particles are coated with an electrically insulating oxide film when exposed to the ambient atmosphere. These oxide films break down only when a given voltage is applied. Elements such as silicon and boron may also be used.

Suitable oxidizing agents are all those compounds which produce oxygen upon reaction, such as halogenates, perhalogenates, nitrates, higher oxides and peroxides, chr0- mates, manganates, perchromates and permanganates; particularly suitable substances are, for example, alkali perchlorates and -nitrates.

The electrically conducting oxides, such as CuO, NiO, MnO or Pb0 may be used as semiconductor materials. A few of these oxides, such as MnO and PbO may be used at the same time as oxidizing agent. However, these oxides cannot be the only oxidizing agent in the ignition mass in the flash lamps according to the invention, since in this case the resistance of the mass becomes unduly low, which, when the lamps are arranged in a holder, gives rise to failing lamps and to double ignition. Another disadvantage is that in this case the reaction in the ignition mass produces too many light-absorbing compounds which reduce the light output of the flash lamp.

Particularly suitable semiconductor materials are complex oxides, such as electrically conducting spinels and perovskites.

Such a complex oxide is, for example, lanthanum cobaltite, in which part of the lanthanum is replaced by strontium.

Suitable binders are solid organic polymers, such as nitrocellulose and polymethylmethacrylate.

The activator may consist, for example, of red phosphorus, sulphur or selenium. In order to obtain ignition masses having optimum properties, it has been found to be desirable for the grain sizes of the various constituents of the mass not to be excessively different. A suitable grain size is of the order of 10 microns.

A satisfactory operation of the ignition mass in flash lamps according to the invention can be obtained only if the constituents of the ignition mass are thoroughly mixed.

The voltage at which breakdown occurs will then not be excessively different for each individual lamp.

The constituents are stirred with a volatile organic solvent to form a usable paste. The paste is provided on the ends of the lead-in wires and the solvent is then expelled, for example, by moderate heating.

Ignition masses have been prepared, for example, having compositions as indicated in the table (in percent by Weight):

Composition The substances mentioned in the table were thoroughly mixed while adding 30 to 40% by weight of a solvent, for example, lactic acid ethylester or methylglycolacetate, to form a usable paste.

The cobaltite mentioned in the table had a composition La Sr Co0 and the nitrocellulose was of the estersoluble type.

After evaporation of the solvent, the resistance of the compositions mentioned in the table, measured at 22 v., is in the lamp approximately M9 and more, while the ignition takes place between approximately 1000 and 2800 v. and generally between 1500 and 2500 v. In this case, a holder which accommodates eight parallel-connected flash lamps and which is connected to a voltage source supplying a maximum voltage of 3200 v. operates without lamps failing to ignite or two or more lamps being ignited simultaneously. With the compositions B and D, the same results were obtained if the voltage source supplied a maximum voltage of 2200 v. According to a feature of the invention, it has been found that these results can be obtained only if the flash lamps in accordance with the invention means which prevent the formation of current bridges in the flash lamp between the lead-in wires by electrically conducting combustion products. The electrically conducting combustion products may consist of particles of the metal wool which have not completely reacted with the gas atmosphere; the electrically conducting particles of the ignition mass may also contribute to the formation of current bridges.

If such current bridges have formed in a lamp which has been ignited and if this flash lamp is arranged in a holder in which the flash lamps are connected in parallel, this may result in that, when a next flash lamp should be ignited, the voltage across these current bridges decreases to a value at which a next flash lamp in the holder can no longer be ignited.

The formation of current bridges may be prevented by ensuring that the lamp includes means which screen part of the bulb wall around one or both lead-in wires from deposition of electrically conducting combustion products. It is also required that the lead-in wires not be interconnected, as in many known lamp types, by means of a head on which a current bridge can be formed by combustion products between the ends of the lead-in wires. After it has been found that the formation of current bridges is an apparent cause of combustion flash lamps arranged in a holder in parallel connection failing to ignite, a number of means can be devised in a simple manner to prevent the formation of current bridges. Some of these means, which have proved satisfactory in practice, will be described more fully hereinafter.

During the investigations leading to the invention, it has been found that water which is formed upon combustion of the hinder or which is released upon ignition from the lacquer layer applied to the outer side of the bulb wall as a safety measure and is drawn into the lamp, may contribute to the formation of current bridges. It is known that cracks are formed in the bulb walls or" most combustion flash lamps during ignition, while moreover, a subatmospheric pressure prevails in the lamp after ignition. After ignition, the ambient atmosphere may thus be drawn into the lamp.

In this connection, it has proved advantageous to use an oxidizing agent which, when supplying oxygen, passes into a water-binding substance such as Ca(ClO which forms CaCl A small quantity of drying agent, for example, 10 mg. of silica gel, may also be introduced into the lamp.

The invention will now be described more fully, by way of example with reference to the drawings. In the drawings:

FIGURES 1, 2 and 3 are sectional views of embodiments of flash lamps according to the invention.

FIGURE 4 shows a circuit diagram including a number of flash lamps according to the invention.

FIGURE 5 shows a curve indicating the voltage variation as a function of time.

FIGURE 6 shows an embodiment of a holder which accommodates a number of lamps.

FIGURE 7 shows flux-time curves of a flash lamp according to the invention and of a conventional flash lamp.

FIGURE 1 is a diagrammatic sectional view of an embodiment of a flash lamp according to the invention. The

lamp comprises a glass bulb 1 which is provided on its lower side with a pinch 2 through which are passed lead-in wires 3 and 4. Inside the bulb 1, the lead-in wires 3 and 4 are passed through glass beads 5 and 5A, respectively, which are provided as low as possible in the bulb, while the lead-in wires are coated with glass below the beads 3A, 4A. The upper sides of the beads 5 and 5A are coated with an ignition mass 6 which is in contact with the ends 7 and 8 of the lead-in wires 3 and 4 and interconnects these wires electrically. The bulb 1 further contains a metal wool 9, for example, of zirconium and an oxidizing gas capable of reacting with the metal wool after ignition, such as oxygen, nitrogen fluorides (NF N F4), oxygen fluoride 2)- The reference numerals of FIGURES 2 and 3 have the same meaning as in FIGURE 1. However, in FIGURE 2, only one lead-in wire 3 is provided with a bead 5. At the instant at which the ignition mass 6 has burned completely, there is no longer a current bridge between the ends 7 and 8 of the lead-in wires 3 and 4. New current bridges cannot be formed. The head in the flash lamp of FIGURE 2 screens the part of the bulb wall 1 around the area at which the lead-in wire enters the bulb from deposition of combustion products. The distance between bead and bulb wall is, for example, smaller than or at the most equal to 1 mm. The risk of a current bridge forming on the bulb wall 1 between the lead-in wires 3 and 4 is thus strongly reduced. The bulb further contains grains of silica gel 6A.

The risk is even smaller if, as in the flash lamp of FIG- URE 3, the lead-in wires 3 and -4 are each provided with a bead '5 and 5A.

FIGURE 4 shows a circuit diagram.

In this circuit diagram, the high-voltage source comprises a battery 1 one terminal of which is connected through the series-combination of a resistor 2 and a capacitor 3 to a termianl of the low-voltage winding 4A of the pulse transformer. The other terminal of the battery 1 is connected to the other terminal of the low-voltage winding 4A of the pulse transformer. The circuit includes two switching members. The switching member 5 is mechanically closed at the instant at which the holder accommodating the flash lamps is connected to the high voltage source; thus, the battery is prevented from slowly being discharged. The switching member 6 is coupled with the shutter of the camera. It is closed when the shutter is opened. The holder (indicated diagrammatically by a broken line 7) accommodates five parallel-connected flash lamps 8-12. The lamps are connected to the high-voltage winding 4B of the pulse transformer, as shown in the diagram.

In a practical embodiment, use is made of a battery 1 of 6 v., a resistor 2 of 8509, a capacitor 3 of 200 ,uF and a pulse transformer 4A, 4B the low-voltage winding 4A of which consists of eight turns, while the high-voltage wind- 1 ing 4B consists of eight thousand turns on a magnetizable core. Such a voltage source supplies a voltage of approximately 3000 v. which has approximately the form of a damped sinusoidal oscillation having an oscillation time of the order of 200 microseconds. The energy supplied is then approximately 100 microjoules.

If with closed switching member 5, the switching memher 6 is transiently closed, one of the flash lamps 8-12 will be ignited. When the switching member 6 is closed a next time, a next lamp is ignited. FIGURE 5 shows diagrammatically the voltage variation across the lamps 8 and 12. The curve 13 indicates the voltage variation across the terminals of the high-voltage winding of the pulse transformer. The lines denoted by 8A-12A indicate the decrease of this voltage when, upon each closure of the camera contact, the lamps 8, 11, 9, 12 and are successively ignited. The order of succession is chosen arbitrarily. In practice, the order of succession of the ignition will depend upon the properties of the ignition masses in the various lamps.

As a matter of course, the voltage source may also be constituted by a dynamo or a piezo-electric crystal.

FIGURE 6 is an elevation of a holder accommodating flash lamps according to the invention. The holder consists of a base strip 20 of synthetic resin in which slots are recessed for inserting the flash lamps 22. Two metal strips, one of which (21) is shown in the figure, are arranged at right angles to the slots and in the longitudinal direction of the base plate so as to cover two sides of said slots. Behind the flash lamps 22 is arranged a reflector 23 comprising a strip of metal foil folded into the shape shown. The assembly is surrounded by a hood 24 of a transparent synthetic resin which is slipped with clamping fit into the base strip 20. The holder is shown to scale. The strips 21 and the flash lamps together form a parallel arrangement.

In FIGURE 7, the flux current in lumen and the time are plotted against each other. Curve A relates to a flash lamp according to the invention and curve B to a conventional flash lamp. These two lamps contain the same quantity of metal wool of zirconium and oxygen. The effect of the presence or absence of a filament wire and the effect of the location of the ignition mass in the lamp appear from the courses of the curves. The contact time is smaller than 1 millisecond with curve 1 and approximately 2 milliseconds with curve B. The term contact time is employed to signify the time passing between the instant at which the current is switched on and the instant at which a noticeable quantity of actinic light is emitted by the lamp. The maximum time at which the flux current is at a maximum is 8 to 9 milliseconds with curve A and 13 to 15 milliseconds with curve B. The quantity of emitted light in lumen/sec. in all is approximately 10% larger with the flash lamp according to the invention (curve A) than with a conventional flash lamp (curve B).

The combustion flash lamps according to the invention have the following advantages:

The ignition mass can be arranged in the lower part of the lamp; the parts of the lead-in wires located inside the bulb may therefore be extremely small when compared with the conventional combustion flash lamps in which a filament wire is coated with ignition paste. In practice, this advantage and the absence of a filament wire result in that combustion flash lamps can be manufactured in accordance with the invention which emit a quantity of light exceeding by approximately 10% that emitted by flash lamps which include a filament wire coated with ignition paste and which contain the same quantity of actinically burning material. Moreover, the combustion flash lamps according to the invention can be manufactured in a simpler manner and at lower costs than the conventional combustion flash lamps.

The flux-time curve of the combustion flash lamps according to the invention is particularly favorable when compared with the flux-time curve of similar flash lamps which are ignited by ignition paste on a filament wire. The ignition mass in the combustion flash lamps according to the invention ignites the actinically combustible material in the lamp more rapidly than the ignition mass in a conventional combustion flash lamp in which the ignition cannot take place before the filament wire has attained a sutficiently high temperature. This contact time is generally a few milliseconds with the conventional flash lamps and less than 1 millisecond with flash lamps according to the invention. This means that, when combustion flash lamps according to the invention are used, the times of exposure may be chosen to be shorter while retaining the adjustment of the X-contact.

A further advantage of the combustion flash lamp according to the invention is that, in the case of ignition by a high voltage, contact resistances resulting from corrosion of contact points substantially do not influence the ignitability of the flash lamps.

The combustion flash lamps according to the invention may be used advantageously in a holder in which the flash lamps are arranged in parallel connection. In such an arrangement, flash lamps failing to ignite for some reason or other remain in the holder.

The holder may be of a particularly simple and cheap construction. In contradistinction to series arrangement, no special switching members are required. The holder may be designed for one-time use.

Experiments have shown that such holders in conjunction with a high-voltage generator can be used in combination with substantially all the cameras which are commercially available. As a matter of course, it is not necessary for the combustion flash lamps according to the invention to be used in a holder. As an alternative, they may be used in conventional photoflashing apparatus provided that these apparatus are designed for highvoltage ignition.

What is claimed is:

1. A combustion flash lamp comprising, in combination a bulb of transparent material which contains a combustible metal wool and an oxidizing gas which, upon reaction, supply actinic light, and an electric ignition mechanism comprisng lead-in wires for connecting the bulb to an external voltage source and which are interconnected inside the bulb by means of an ignition mass comprising an oxidizable conductive material, a semiconductor material and a binder, and means which screen part of the bulb wall around at least one of the lead-in wires from deposition of combustion products.

2. A combustion flash lamp as claimed in claim 1, wherein the ignition mass contains an oxidizable material and an oxidizing agent in substantially stoichiometric quantities.

3. A combustion flash lamp as claimed in claim 1, wherein the semiconductor material consists of lanthanum cobaltite in which part of the lanthanum is replaced by strontium.

4. A combustion flash lamp as claimed in claim 1, wherein the ignition mass contains an activator consisting of an element selected from the group consisting of phosphorus, sulfur, and selenium.

5. A combustion flash lamp as claimed in claim 1, wherein only one of the lead-in wires of the lamp is provided with a bead.

6. A combustion flash lamp as claimed in claim 1, wherein each of the lead-in wires of the lamp is provided with a head.

7. A combustion flash lamp as claimed in claim 1, wherein the lamp contains a drying agent.

8. A combustion flash lamp as claimed in claim 1, wherein the ignition mass contains an oxidizing agent which constitutes a drying agent when supplying oxygen.

9. A combustion flash lamp as claimed in claim 1 in which the oxidizable conductive material is a metal powder superficially coated with a thin oxide layer.

10. A combustion flash lamp as claimed in claim 9 in which the metal powder is an element selected from the group consisting of aluminum, magnesium, zirconium,

lanthanum, titanium, niobium, thorium, silicon, and boron.

11. A combustion flash lamp as claimed in claim 9 in which the oxdizing agent is selected from the group consisting of halogenates, perhalogenates, nitrates, oxides, peroxides, chromates, manganates, perchronrates and permanganates.

12. A combustion flash lamp as claimed in claim 11 in which the oxidizing agent is an alkali perchlorate.

13. A combustion flash lamp as claimed in claim 11 in which the oxidizing agent is an alkali nitrate.

14. A combustion flash lamp as claimed in claim 9 in which the semi-conductor material is selected from the group consisting of CuO, NiO, MnO and PbO 15. A photographic exposure device comprising, in combination, a plurality of combustion flash lamps, and means to electrically ignite each of said lamps in succession including means to generate and apply a transient igniting voltage to said lamps, and means connecting said lamps in parallel, each of said lamps comprising a light transparent envelope containing a combustible metal and an oxidizing gas therein which upon reaction generate actinic light and and lead-in wires which are connected to said ignition means and have a portion thereof within the interior of said envelope, means within said envelope for interconnecting said lead-in wires and which with the application of the transient ignition voltage between said lead-in Wires produces a reaction between said metal wool and said oxidizing gas, said means interconnecting said lead-in wires being constituted of an oxidizable conductive material, a semi-conductor material, and a binder, said means having a breakdown potential equal to said ignition voltage whereby with the application of the ignition voltage to the lead-in conductors said means initially rapidly breaks down electrically and the resistance thereof decreases thereafter with ignition of the metal wool preventing ignition of another lamp until a second transient ignition voltage is applied.

16. A device as claimed in claim 15 in which each lamp contains an activator which causes the ignition mass to react rapidly as the temperature increases.

17. A device as claimed in claim 15 in which the means for generating and applying a transient igniting voltage is a generator which produces strongly damped oscillations.

18. A device as claimed in claim 17 in which the ignition voltage is between A and A of the maximum voltage supplied by the generator.

19. A device as claimed in claim 16 in which the activator is an element selected from the group consisting of phosphorus, sulfur, and selenium.

References Cited UNITED STATES PATENTS 2,771,765 11/1956 Amott et a1. 431 3,312,085 4/1967 Schilling et al 431-95 OHARLES J. MYHRE, Primary Examiner 

